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Journal of Bacteriology, April 1999, p. 2067-2074, Vol. 181, No. 7
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

HmbR, a Hemoglobin-Binding Outer Membrane Protein of Neisseria meningitidis, Undergoes Phase Variation

Anthony R. Richardson and Igor Stojiljkovic*

Department of Microbiology and Immunology, Emory University School of Medicine, 3001 Rollins Research Center, Atlanta, Georgia 30322

Received 30 October 1998/Accepted 23 January 1999

Neisseria meningitidis uses hemoglobin (Hb) as an iron source via two TonB-dependent outer membrane receptors, HmbR and HpuB. Analysis of 25 epidemiologically unrelated clinical isolates from serogroups A, B, C, and Y revealed that 64% strains possessed both Hb receptor genes. Examination of the hmbR expression pattern in strains in which the hpuB gene was genetically inactivated revealed two distinct Hb utilization phenotypes. Five strains retained the ability to grow as a confluent lawn, while seven grew only as single colonies around Hb discs. The single-colony phenotype observed for some hpuB mutants is suggestive of phase variation of hmbR. The length of the poly(G) tract starting at position +1164 of hmbR absolutely correlated with the two Hb utilization phenotypes. All five strains that grew as confluent lawns around Hb discs possessed either 9 or 12 consecutive G residues. All seven strains that grew as single colonies around Hb discs had poly(G) tracts of a length other than 9 or 12. These single-colony variants that arose around the Hb discs had poly(G) tracts with either 9 or 12 consecutive G residues restoring the hmbR reading frame. Inactivation of hmbR in these strains resulted in a loss of Hb utilization, demonstrating that the change in the hmbR gene was responsible for the phenotypic switch. The switching rates from hmbR phase off to phase on were ~5 × 10-4 in four serogroup C strains, 2 × 10-2 in the serogroup A isolate, and 7 × 10-6 in the serogroup B isolate.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, Emory University School of Medicine, 3001 Rollins Research Center, 1510 Clifton Rd. NE, Atlanta, GA 30322. Phone: (404) 727-1322. Fax: (404) 727-8250. E-mail: stojiljk{at}microbio1.microbio.emory.edu.

Journal of Bacteriology, April 1999, p. 2067-2074, Vol. 181, No. 7
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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